Photovoltaic cell, method for assembling plurality of cells and assembly of a plurality of photovoltaic cells

ABSTRACT

The photovoltaic cell has a block that includes at least one semiconductor substrate in which is formed at least one photovoltaic junction that is connected to a first electrical contact element of a first pole and to a second electrical contact element of a second pole. The cell includes a first transparent cover that is placed on a first surface of the block and defines with the block of the cell a first recess groove of a first electrically conductive wire element.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a photovoltaic cell provided with a block including at least one semiconductor substrate in which is formed at least one photovoltaic junction connected to a first electrical contact element with a first pole and to a second electrical contact element with a second pole.

STATE OF THE ART

Current photovoltaic panels comprise lines of solar cells electrically connected in series.

FIG. 1 represents three solar cells 1 a, 1 b, 1 c connected in series. A cell comprises a semiconductor substrate 2 a in which at least one junction PN is formed. A cell has usually the form of a square with a side of approximately 16 cm. The electrical contact elements are arranged on both sides of the substrate 2 a. In FIG. 1, a first electrical contact element 3 with a negative pole is arranged on the face of each cell 1 a, 1 b, 1 c designed to be oriented towards the sun. In order to increase the yield of a solar cell while letting photons through, the first electrical contact element 3 is constituted by an electrode provided on both sides of its longitudinal axis of combs. A second electrical contact element with a positive pole is formed by a metal layer 4 covering the back face of the cell. A series of solar cells is made by welding electrically conducting bands 5 a, 5 b, 5 c between two adjacent cells. Thus, a first cell 1 a is linked to a second cell 1 b by a band 5 b welded at one end to the metal layer 4 of the second cell 1 b and at another end to the first electrical contact element 3 of the first cell 1 a. The second cell 1 b is connected to a third cell 1 c by a band 5 b welded at one end to the metal layer 4 of the third cell 1 c and at another end to the first electrical contact element 3 of the second cell 1 b. The step which consists in linking several cells together becomes increasingly difficult to carry out since current technologies tend to make cells thinner in order to save materials, in particular when they are made on silicon substrates.

Indeed, the rigid solar cells are to date mainly produced from increasingly fine silicon plates. Materials and manufacturing processes are the subject of research programs in order to reduce the production costs by diminishing the quantity of silicon per wafer. For that, the thickness of the silicon wafers has been first of all reduced from 300 μm to 200 μm, and it is now thought to reach a thickness of 180 μm, even 150 μm. As result of this reduction in thickness, the cells has become more and more fragile and their handling difficult.

Moreover, once the cells are connected together to form a panel, the panel is encapsulated within a massive framework in order to protect the whole. The final panel is often relatively thick.

In addition, making flexible solar panels requires in a general way the use of “flexible” semiconductor materials whose performance is lower than that of “rigid” semiconductor materials such as single-crystal silicon.

OBJECT OF THE INVENTION

The object of the invention consists in making a photovoltaic cell easy to conceive and to handle, while allowing to make flexible assemblies with low thicknesses.

This object is reached in that the cell comprises a first transparent cover arranged on a first face of the block and delimiting with said cell block a first groove for housing a first electrically conducting wire element.

According to one embodiment the cell comprises a second cover arranged on a second face of the block, opposite the first face of the block, and delimiting with the cell block a second groove for housing a second electrically conducting wire element.

According to an alternative, the second cover and/or first cover are placed directly on the semiconductor substrate.

According to another embodiment, at least one of the electrical contact elements connected to the photovoltaic junction comprises a wire element embedded in a groove.

-   -   According to another embodiment, at least one of the electrical         contact elements comprises a plurality of conducting arms         arranged on a face of the semiconductor substrate, said arms         being designed to be in contact with or to be linked to a wire         element.

According to another embodiment, as the second cover is transparent, the block comprises two semiconductor substrates including photovoltaic junctions separated by a metal layer, the cell comprising a third longitudinal groove for housing a third electrically conducting wire element designed to be connected to said metal layer.

According to another embodiment, the block comprises two semiconductor substrates including photovoltaic junctions separated by a dielectric, the cell comprising third and fourth grooves respectively formed on a side face at the interface between the dielectric layer and the associated semiconductor substrates.

Another object of the invention consists of an assembly of photovoltaic cells including several photovoltaic cells linked to one another by several wire elements, each wire element being embedded in the grooves of at least two photovoltaic cells.

Another object of the invention consists of a method for assembling a plurality of photovoltaic cells, each cell comprising first and second grooves formed on the same side face, the method comprises the following successive steps:

-   -   positioning cells in the form of at least one line so as to form         a first and a second lines of grooves, the first groove of one         cell being aligned with the second groove of the adjacent cell,     -   wiring each line of cells, a first electrically conducting wire         being inserted into each groove of the first line of grooves,         and a second electrically conducting wire being inserted into         each groove of the second line of grooves,     -   alternatively cutting first and second wires between two         adjacent cells,     -   reversing every second photovoltaic cell in order to orient all         the first covers of the photovoltaic cells towards the same         side.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and characteristics will more clearly arise from the following description of particular embodiments of the invention given as nonrestrictive examples and represented in the annexed drawings in which:

FIG. 1 illustrates three solar cells connected according to a known technique of the prior art.

FIG. 2 illustrates a first embodiment of a photovoltaic cell according to the invention.

FIG. 3 illustrates a top view of the cell in FIG. 2.

FIG. 4 illustrates an alternative of the first embodiment.

FIG. 5 illustrates a second embodiment of a cell according to the invention.

FIG. 6 illustrates an alternative of the second embodiment.

FIG. 7 illustrates a third embodiment of a photovoltaic cell provided with three grooves.

FIG. 8 illustrates a fourth embodiment of a photovoltaic cell according to the invention.

FIG. 9 illustrates a fifth embodiment of a photovoltaic cell according to the invention.

FIGS. 10 to 16 illustrate a method for assembling a plurality of photovoltaic cells in the form of a line.

FIG. 17 illustrates an implementation alternative of the method for assembling a plurality of photovoltaic cells.

FIG. 18 illustrates a plurality of photovoltaic cells arranged in the form of matrix.

FIGS. 19 to 22 illustrate an example of a method for manufacturing photovoltaic cells.

DESCRIPTION OF PREFERENTIAL EMBODIMENTS

In the embodiments illustrated in FIGS. 2 to 9, a photovoltaic cell is provided with a block 2 including at least one semiconductor substrate 2 a in which at least one photovoltaic junction is formed. A photovoltaic junction can consist of a junction PN. Each photovoltaic junction is connected to a first electrical contact element with a first pole and to a second electrical contact element with a second pole. The photovoltaic cell comprises a first transparent cover 6 a arranged on a first face of the block 2 and delimiting with the block 2 a first groove 7 a for housing a first electrically conducting wire element.

Preferably, the first groove 7 a is a longitudinal groove for housing the first wire element on a side face 8 of the cell.

The first and second poles correspond, for example, to an anode and a cathode. The first and second electrical contact elements allow the collection of the charges, electrons and holes of electrons, generated in the semiconductor substrate.

The cover 6 a preferably comprises a shoulder at one of its longitudinal edges. The block 2 preferably has dimensions appreciably equal to the dimensions of the first cover 6 a. Thus, when the first cover 6 a is in position on the block 2 as illustrated in FIG. 2, and the face of the first cover 6 a with a notch forming the shoulder is oriented towards the first face of the block 2, the first longitudinal groove 7 a is naturally delimited. The first groove 7 a is then made of a bottom 9 a linked to two side walls 9 b, 9 c. The side wall 9 b and the bottom 9 a are delimited by the shoulder of the first cover 6 a and the other side wall 9 c is delimited by a free portion of the first face of the block 2.

The first wire element is preferably embedded longitudinally in the first groove 7 a. By longitudinal embedding it is understood that the axis of the wire element is substantially parallel to the longitudinal axis of the groove in which it is embedded.

According to a first particular embodiment illustrated in FIGS. 2 and 3, the block 2 is made up of only one semiconductor substrate and the first cover 6 a can be placed directly on the semiconductor substrate. The first electrical contact element can comprise a plurality of conducting arms 10 arranged on a first face of the substrate. The second electrical contact element can comprise a metal layer 4 formed on a second face of the semiconductor substrate opposite the first face of the substrate. In other words, the metal layer 4 covers the semiconductor substrate. Preferably, the arms 10 are substantially perpendicular to a longitudinal axis of the first groove 7 a, and are arranged between the first cover 6 a and the first face of the substrate. Preferably, the arms are electrically connected to the groove by means of an electrically conducting connection arm (not represented) covering at least a part of the side wall 9 c of the first groove 7 a formed by the portion of substrate. The arms 10 are preferably placed at a distance to one another so as to optimize the active surface of the cell. In other words, at least one of the electrical contact elements comprises a plurality of conducting arms 10 arranged on a face of the semiconductor substrate, said arms 10 being designed to be in contact with or to be linked to a wire element.

The arms 10 and the connection arm can be made out of a metal or another conducting material deposited, or formed, on the substrate 2.

According to an alternative, the connection arm is not necessary, the arms 10 cover a part of the side wall 9 c of the first groove 7 a formed by the free portion of the semiconductor substrate. The arms 10 are electrically connected together when the first electrically conducting wire element is embedded longitudinally in the first groove 7 a. When said first wire element is in electrical contact with the substrate, for example when the wire is made up of only one conducting material, said first wire element then constitutes a part of the first of contact element. In other words, at least one of the electrical contact elements connected to the photovoltaic junction comprises a wire element embedded in a groove.

According to another alternative, if the cell, and more particularly the semiconductor substrate, has dimensions lower than a minimal distance making it possible to attract a great number of electrons or holes of electrons generated by the absorption of photons, the arms 10 are then not essential. The first electrically conducting wire element, once it is longitudinally embedded in the first groove 7 a, can alone act as the first electrical contact element.

An assembly of such cells in series with electrically conducting wire elements comprises, between each cell, a electrically wire element connecting the first groove 7 a of a first cell to the metal layer 4 of a second cell.

According to an alternative of the first embodiment illustrated in FIG. 4, the free face of the metal layer 4 is covered by a second cover 6 b in the center of which a second groove 7 b is made, preferably with a longitudinal axis substantially parallel to the longitudinal axis of the first groove 7 a. This second groove 7 b makes it possible to facilitate the assembly of a series of cells by delimiting a groove in which a second electrically conducting wire element can be inserted, for example by longitudinal embedding. As in FIG. 4, the cell can comprise a second cover 6 b arranged on a second face of the block 2, opposite the first face of the block 2, and delimiting with the block 2 of the cell a second groove 7 b for housing a second electrically conducting wire element.

Of course, if the cell has small dimensions, the metal layer can be removed and the second electrical contact element is then formed by the second electrically conducting wire element in contact with the substrate. In this case, only the second cover 6 b remains to protect the semiconductor substrate.

According to another alternative not represented, the metal layer 4 is sufficiently thick to make the second groove 7 b in the free face of this metal layer 4. The cover 6 b is then not essential.

According to a second embodiment illustrated in FIG. 5 and in which the block 2 comprises a single semiconductor substrate provided with a photovoltaic junction, the cell comprises a second cover 6 b arranged on a second face of the semiconductor substrate, opposite the first face of said substrate, and delimiting with the substrate, preferably in a side face 8 of the cell, a second longitudinal groove 7 b for housing a second electrically conducting wire element. This second groove 7 b is preferably substantially parallel to the first groove 7 a, i.e. it has a longitudinal axis parallel to the longitudinal axis of the first groove 7 a. The second groove 7 b is preferably located in the same side face 8 as the first groove 7 a to facilitate the method of assembling a plurality of cells, as it is described hereafter in relation to FIGS. 12 and 13. The first and second electrical contact elements can be totally or partly composed of at least the first and second wire elements respectively longitudinally embedded in the first 7 a and second 7 b grooves.

In FIG. 5, a metal layer 4 is preferably interposed between the semiconductor substrate and the second cover 6 b in order to totally or partly form the second electrical contact element, said metal layer 4 being in electrical contact with the second wire element after its embedding into the second groove 7 b. As described previously, the embodiment in FIG. 5 can also integrate arms arranged between the first cover 6 a and the semiconductor substrate.

According to an alternative of the second embodiment illustrated in FIG. 6, the second cover 6 b is transparent too. This makes it possible to collect charges produced by photons interacting in the semiconductor while going through the first cover 6 a and/or the second cover 6 b. Consequently the metal layer 4 can be replaced by arms, similar to the previously-described arms 10, and interposed between the second cover 6 b and the semiconductor substrate. The conducting arms are, for example, perpendicular to a longitudinal axis of the second groove 7 b. The conducting arms can be electrically connected together by a conducting connection arm. This connection arm is preferably placed under the future embedded wire element, i.e. on the side wall of the second groove 7 b formed by the portion of substrate, in order not to increase the obstruction to photons induced by the presence of the conducting arms on the surface of the substrate and the presence of the future wire element.

As indicated previously, if the cell has small dimensions, the arms are not essential. The first and second electrically conducting wire elements, respectively longitudinally embedded in the first and second grooves 7 a, 7 b, can form alone the first and second electrical contact elements. Consequently, the first 6 a and/or the second 6 b covers can be placed directly on the semiconductor substrate.

According to a third embodiment illustrated in FIG. 7, the cell includes a central block 2 sandwiched between two covers 6 a, 6 b. More precisely, the cell includes a stack composed of a first transparent cover 6 a, of a first semiconductor substrate 2 a provided with a first photovoltaic junction, of a metal layer 4, of a second semiconductor substrate 2 b provided with a second photovoltaic junction, and of a second transparent cover 6 b. The first cover 6 a and the semiconductor substrate 2 a delimit on a side face 8 of the cell a first longitudinal groove 7 a for housing an electrically conducting wire element. The second cover 6 b and the semiconductor substrate 2 b delimit on a side face 8 of the cell a second longitudinal groove 7 b for housing a second electrically conducting wire element. Moreover, the first 2 a and second 2 b semiconductor substrates are, in this example, larger than the metal layer 4 on the side of the side face 8. Thus, the metal layer 4 and the first and second substrates 2 a, 2 b delimit on the side face 8 of the cell a third longitudinal groove 7 c for housing a third electrically conducting wire element designed to be linked to the metal layer 4. In other words, as the second cover 6 b is transparent, the block 2 comprises two semiconductor substrates 2 a, 2 b including photovoltaic junctions separated by a metal layer 4, the cell moreover comprising a third longitudinal groove 7 c for housing a third electrically conducting wire element designed to be linked to said metal layer 4. The third groove 7 c comprises a longitudinal axis, preferably substantially parallel to the longitudinal axis of the first groove 7 a. Preferably, the three grooves 7 a, 7 b, 7 c are formed in the same side face 8 of the cell to facilitate its assembly with other cells. Such a cell can receive photons from the two main faces of the cell.

Preferably, conducting arms similar to those indicated for the embodiment illustrated in FIG. 6 are respectively interposed between the first cover 6 a and the substrate 2 a, and between the second cover 6 b and the substrate 2 b. Of course, if the cell has small dimensions, the arms are not essential.

In this embodiment (FIG. 7), the cell includes two photovoltaic junctions formed respectively in the semiconductor substrates 2 a and 2 b. Each photovoltaic junction is connected to a first and a second electrical contact element. The third wire element, placed in the third groove 7 c, will be linked to a contact element of the upper photovoltaic junction (in the substrate 2 b) and to a contact element of the lower photovoltaic junction (in the substrate 2 a). According to the connections that will be carried out via the first, second and third wire elements embedded in the grooves of the cell, the two photovoltaic junctions can finally be mounted in series or in parallel.

According to an alternative, if the cell has small dimensions, the metal layer 4 can be replaced by a dielectric. The third groove 7 c is then delimited by the dielectric and two opposite portions of the semiconductor substrates 2 a and 2 b. The wire element inserted in the third groove 7 c forms a electrical contact element common to both photovoltaic junctions.

An assembly example for several cells such as those in FIG. 7 is described hereafter. It is used a Y-shaped electrically conducting wire element with two secondary arms connected to a main arm. The secondary arms are respectively inserted into the first and second grooves 7 a, 7 b of a cell. The main arm of the Y-shaped wire element will be embedded in the third groove 7 c of an adjacent cell. The two photovoltaic junctions 2 a, 2 b of each cell are then mounted in parallel and the cell is equivalent to a single junction connected to common first and second poles.

In such an assembly, the Y-shaped wire element can be composed of two wires meeting at the third groove to form the main arm of the Y.

According to a fourth embodiment illustrated in FIG. 8, the cell always comprises first and second transparent covers 6 a, 6 b, each of them delimiting with a central block 2 a longitudinal groove for housing a wire element 7 a, 7 b. The block 2 comprises two semiconductor substrates 2 a, 2 b including photovoltaic junctions, separated by a dielectric 2 c. A third longitudinal groove 7 c and a fourth longitudinal groove 7 d, preferably substantially parallel to the first groove 7 a, are formed respectively at the interfaces between the dielectric layer 2 c and the associated semiconductor substrates 2 a, 2 b. Preferably, the third 7 c and fourth 7 d grooves are made in the same side face of the cell as the first and second grooves 7 a, 7 b.

Moreover, the block 2 can comprise the metal layers 4 a, 4 b interposed between the semiconductor substrates 2 a, 2 b and the dielectric 2 c on both sides of the dielectric 2 c. The metal layers 4 a, 4 b enable to optimize the yield of a cell if its dimensions do not allow the wire elements to collect all the charges generated in the semiconductor substrates.

According to an alternative applicable to all the embodiments, each cover 6 a, 6 b can form a concentrator of the solar radiations towards the associated semiconductor substrate. This makes it possible to improve the yield of each photovoltaic cell. As a particular example, a transparent cover can comprise a plurality of lenses making the photons converge into the associated semiconductor substrate.

In a general way, the yield of the cell falls when the semiconductor heats. Thus, at least one of the covers can form a heat sink, while using, for example, a comb-shaped cover made out of a thermo-conducting material. For example, a concentrating transparent cover and a heat sink cover can be envisaged.

According to a fifth embodiment illustrated in FIG. 9, the cell is of the type of those illustrated in FIGS. 5 and 6, i.e. it comprises on a first side face 8 a first and second grooves 7 a, 7 b. The cell in FIG. 9 moreover comprises on a second face side 8 b, opposite and preferably parallel to the first side face 8 a, longitudinal third and fourth grooves 7 c, 7 d for housing a wire element. These grooves 7 c, 7 d are preferably also delimited by a shoulder in the associated cover and by the semiconductor substrate. The assembly of two cells in series can be carried out by a first wire element inserted both in the first groove 7 a of a first cell and in the second groove 7 b of a second cell. In the same way a second wire element is inserted both in the third groove 7 c of the first cell and in the fourth groove 7 d of the second cell. This makes it possible to obtain a series of cells maintained on two opposite side faces thus improving the solidity of the assembly. Moreover, if one of the wire elements breaks, the second will still be able to ensure the continuity in the series of cells. According to the dimensions of the cells, these wire elements can be sufficient for forming the first and second electrical contact elements. If not, it is possible to form arms between each cover and the substrate as previously described. Of course, the person skilled in the art can adapt this principle to the embodiments in FIGS. 7 and 8.

Thanks to such cells, the semiconductor substrate is protected from the external environment by the two covers 6 a, 6 b or by the first transparent cover 6 a and the metal layer 4 formed under the cell. Thus, contrary to the methods for assembling traditional photovoltaic cells, it is not necessary to assemble the various photovoltaic cells according to the invention in a specific environment with few dust (in order to avoid the contamination of the semiconductor substrates).

Moreover, the covers 6 a, 6 b give a certain rigidity to the whole, and allow an easier handling of the cells during the assembly. As an example, the thickness of the semiconductor substrate is about 200 μm and each cover has a thickness of 200 μm.

A plurality of cells as described can be assembled in order to form a flexible photovoltaic panel, being able to be incorporated into a fabric. The flexibility of the panel is made possible by the use of a plurality of cells of small size, preferably with a side lower than 5 mm.

In a general way, an assembly of photovoltaic cells comprises several photovoltaic cells connected to one another by several wire elements, each wire element being embedded in the grooves of at least two photovoltaic cells.

Moreover, the assembling method according to the present invention makes it possible to make photovoltaic panels of very small dimensions comprising some cells of small size.

In the particular case when the cells are able to collect the solar radiations on both sides (by two transparent caps), an assembly of such cells comprises a first face designed to be oriented towards the sun. Reflecting means can be arranged on the second face of the assembly. Indeed, when the first face is oriented towards the solar radiations, a part of the solar radiations goes between the cells and is not absorbed via the first face. The reflecting means then make it possible to collect these radiations and to give them back towards the transparent covers of the second face. Such means can be formed, for example, by an aluminum or silver foil, patterned or not.

According to a particular embodiment example of a assembly using cells comprising in the same side face two longitudinal grooves for housing wire elements, illustrated in FIGS. 10 and 11, the cells are first of all positioned in the form of at least one line so as to form first and second rows of grooves. The cells are arranged so that the first groove 7 a of a cell is aligned with the second groove 7 b of the adjacent cell. As illustrated in FIG. 11, the cells have preferably the same size and form.

The particular example illustrates four cells A, B, C, D, each of them comprising two longitudinal grooves 7 a, 7 b on a side face of the photovoltaic cell. In FIG. 10, the cell A and the cell C have their first transparent cover 6 a oriented towards the top, while the cells B and D have their first transparent cover 6 a directed downwards. This is why the first row of grooves (top row in FIG. 10) is composed (from left to right) of the first groove 7 a of the photovoltaic cell A, the second groove 7 b of the photovoltaic cell B, of the first groove 7 a of the photovoltaic cell C and of the second groove 7 b of the photovoltaic cell D. In the same way, the second row of grooves (bottom row in FIG. 10) is composed (from left to right) of the second groove 7 b of the photovoltaic cell A, of the first groove 7 a of the photovoltaic cell B, of the second groove 7 b of the photovoltaic cell C and of the first groove 7 a of the photovoltaic cell D.

After positioning the cells suitably, these cells are wired on each line as illustrated in FIGS. 12 and 13. A first electrically conducting wire 11 a is inserted in each groove of the first row of grooves (top grooves in FIG. 12), and a second electrically conducting wire 11 b is inserted in each groove of the second row of grooves (bottom grooves in FIG. 12). Thus, in the particular example, the first wire 11 a extends in the first groove 7 a of the cell A, the second groove 7 b of the cell B, the first groove 7 a of the cell C and the second groove 7 b of the cell D whereas the second wire 11 b extends in the second groove 7 b of the cell A, the first groove 7 a of the cell B, the second groove 7 b of the cell C and the first groove 7 a of the cell D. Then, the first and second wires 11 a and 11 b are alternatively sectioned between two adjacent cells (FIG. 14) in order to form the first and second wire elements of each cell. In fact, the first wire element of a cell forms also the second wire element of the adjacent cell. The first and second wires 11 a, 11 b must be good conductors with low ohmic losses. As an example, it will be used wires out of copper or containing an alloy of silver and copper.

During sectioning, as the particular example in FIG. 14 illustrates it, the first wire 11 a in the grooves in the upper part in FIG. 12 is sectioned between the cells A and B, and between the cells C and D. The second wire 11 b in the low grooves is sectioned between the cells B and C. Finally, two adjacent cells are linked by a single segment of wire forming both the first wire element of a cell and the second wire element of the adjacent cell. The cell A is connected to the cell B by a segment of the second wire 11 b, the cell B being connected to the cell C by a segment of the first wire 11 a and the cell C being connected to the cell D by a segment of the second wire 11 b.

Preferably, in order to avoid any short-circuit, when a wire 11 a, 11 b is sectioned between two adjacent cells, it is cut at the groove of said two adjacent cells as in FIG. 14.

After suitably sectioning the first and second wires 11 a, 11 b, every second photovoltaic cell is turned over (FIG. 15) in order to orient all the first covers of the cells on the same side. By turning over it is understood that the cell carries out a rotation of 180° relative to its initial position along an axis parallel to the first and second wires 11 a and 11 b.

FIGS. 15 and 16 illustrate respectively in a side view and a top view the configuration of the cells after the turning-over step. The position of the cells A and C remains unchanged whereas the position of the cells B and D is reversed. In this configuration, the first covers 6 a of each cell are oriented upwards and all the grooves 7 a are then located in the upper part of the line of cells.

According to an alternative, after the photovoltaic cells are turned over, each line of cells is then stretched to allow the cells of the same line to be alternatively arranged on both sides of a central axis of the line of cells, as illustrated in FIG. 17.

This methods enables to connect in series photovoltaic cells as described in a simplified way and to obtain a flexible assembly.

The yield of a plurality of lines of photovoltaic cells in series can be improved by making an assembly in the form of a matrix. Thus, in an alternative, the assembling method comprises the making of a plurality of identical lines of cells. After the turning-over step, and preferably after the stretching step, the lines are arranged so as to form a matrix of lines and columns of cells as in FIG. 18. Two columns of adjacent cells are separated by an interval. Then, at each interval, a third wire electrically connects the conducting wire elements connecting two adjacent cells of each line of the matrix at this interval.

According to the particular example in FIG. 18, the matrix comprises four lines 12 a, 12 b, 12 c, 12 d arranged so as to form four columns of cells 13 a, 13 b, 13 c, 13 d. The first and second columns 13 a, 13 b, the second and third columns 13 b, 13 c, and the third and fourth columns 13 c, 13 d are each separated from one another by a respective interval Int1, Int2, Int3. At each interval, a third wire 14 a, 14 b, 14 c, is arranged and electrically connected to each line of cells. This electric connection can be carried out by welding the third wire to each segment of wire element linking two adjacent cells of the same line in this interval. Thus, in FIG. 18, each line corresponding to a line in FIG. 17, the wire 14 a links in the interval Int1 the wire elements of each line together, the wire 14 b links in the interval Int2 the wire elements 11 a of each line together and the wire 14 c connects in the interval Int3 the wire elements 11 b of each line together.

In order to limit the losses of performance when one or several cells are shaded, it is possible to use bypass diodes on one or more solar cells. In practice, a photovoltaic cell can be regarded as a current generator in parallel with a diode (formed by the photovoltaic junction of the solar cell), the intensity of the current depending on the incidental illumination of the cell. When the cell is shaded, the current is very low even zero. On a line of photovoltaic cells in series, if a cell is shaded, the current generated by the line of cells cannot circulate in it and the production of current becomes very low or zero. A bypass diode makes it possible to form a derivation of the current in order to limit the impacts of a cell which would be shaded or which could have a defect of design limiting its yield. Several modes of insertion of bypass diodes on an assembly of photovoltaic cells according to the present invention can be considered by the man skilled in the art.

In the case, for example, of an assembly such as that illustrated in FIG. 18, it is possible to add an additional line of bypass diodes, so that each additional diode of this additional line is connected in parallel to all the photovoltaic cells of a column. More precisely, the anode and the cathode of each additional diode are respectively connected to the cathodes and the anodes of the diodes formed by the photovoltaic junctions of the photovoltaic cells of a column. Each of such additional diodes can be made in the form of a microchip having two grooves provided with conducting studs respectively connected to the anode and the cathode of a diode of the respective microchip. The additional diodes can then be connected to one another and to the photovoltaic cells of the assembly according to a method for assembling identical to that described above. Preferably, the dimensions of such microchips are substantially the same as those of the photovoltaic cells of the assembly in order to guarantee a good integration of those into the assembly.

As a particular embodiment example, the diodes used are Schottky diodes. These diodes have the advantage of having a very low voltage drop (approximately 0.3 V) limiting the current consumed by the by-pass.

Such a method makes it possible to manufacture flexible and resilient panels in the form of a matrix of cells. Thus, the panel will be less impacted by zones of shades or at the time of a failure of one of the cells. The best tolerance of this panel allow it to obtain performance increased during its use on nonplane surfaces. As an example, the panel can be integrated into a garment or a backpack, it then makes it possible to store energy for supplying electronics equipments or to recharge batteries. This integration into textiles is not easily to achieve today. Indeed, an existing basic cell on a rigid support has a dimension of approximately 16 cm×16 cm. However, thanks to the assembling method as described, it is possible to obtain from a basic cell about 1024 photovoltaic cells having substantially a square with a side of 5 mm. It is then possible to connect these elements in order to form a matrix of thirty-two lines and thirty-two columns. By using flexible wire elements, it is finally obtained a square with a side of approximately 16 cm with a certain flexibility, which is suitable for its integration into a textile.

The assembly obtained can finally be embedded into a flexible adhesive or encapsulated between two photon transparent layers of flexible plastic. This makes it possible both to protect the components by ensuring a protection against corrosion and water, to keep the flexibility of the assembly, and to avoid the short-circuits between wire when the assembly is stressed.

An example of a method for manufacturing a plurality of photovoltaic cells, such as those illustrated in FIGS. 2 to 9, is illustrated in FIGS. 19 to 22. In a first step, a plurality of active zones 16 are made on an active plate 15. Each active zone 16 comprises at least one photovoltaic junction made out of a semiconductor material. Such a plate can have the form of a silicon wafer on which a plurality of active zones 16 provided with a photovoltaic junction are made.

Then, a back plate 17 made out of a transparent material, for example glass, can be transferred onto the active plate 15 to form an assembly. This back plate 17 comprises cavities 18 arranged so that, for each active zone 16 of the active plate 15, a cavity 18 is placed facing one of the edges of said active zone (FIGS. 19 and 20). In FIG. 20, as the active zones 16 are arranged in an unordered way, the cavities 18 are consequently made in the back plate 17.

Lastly, the assembly is cut out along the edges of the various active zones 16 for forming the cells. The cutting path goes through each cavity to obtain, after cutting, a plurality of cells each comprising at least one lateral groove (FIG. 21).

Preferably, the active zones form a grid as illustrated in FIG. 22 for optimizing the number of active zones made on the active plate. Thus, the cavities 18 of the back plate 17 can be made by a plurality of substantially parallel trenches facilitating the cutting of the assembly.

According to an alternative embodiment of the method, the active plate 15 is covered with an active layer and the cavities 18 of the back plate can be made by a plurality of substantially parallel trenches facilitating the cutting of the assembly. Indeed, the active zone can be a simple PN junction, it is then not necessary to first delimit active zones for each cell.

In order to make photovoltaic cells with two caps, it is possible, before cutting said assembly, to add a second back plate onto the back face of the active plate 15. The back plate on the back face preferably includes cavities, or openings, designed to form after cutting the assembly grooves for housing a wire element respectively placed on a side face or the back face of a cell.

According to an manufacture alternative, the active plate 15 can be thinned by its back face in order to make cells with a low thickness. In the same way, if the active plate 15 includes a metal layer, the metal layer can be thinned.

Once the back plate 17 is integral with the active plate 15, the active plate 15 can be thinned so as to let the active zones 16 flush before the transfer of another back plate onto the back face of the active plate 15. In particular, this enables to make a cell such as illustrated in FIG. 6, i.e. with two transparent caps.

Other embodiments of a photovoltaic cell according to the invention as well as other methods for assembling photovoltaic cells can be imagined by the man skilled in the art. Thus, although in the previously-described examples of cells the covers are placed directly on semiconductor substrates, it is possible to place the covers onto another constitutive layer of the central block. Moreover, one or more grooves for housing a wire element can be made on any face of the photovoltaic cell, for example on the front face of the photovoltaic cell through the transparent cover covering the block of the cell. 

The invention claimed is:
 1. A photovoltaic cell comprising: a block including at least one semiconductor substrate, the semiconductor substrate comprising a first main face, a second main face, a first side face and a second side face, the side faces being orthogonal to the main faces; at least one photovoltaic junction formed in the at least one semiconductor substrate, the at least one photovoltaic junction being connected to a first electrical contact element disposed on the first main face and to a second electrical contact element on the second main face; a first electrically conducting wire element connected to the first electrical contact element or the second electrical contact element; and a first transparent cover arranged on the first main face which includes a first groove in an external face of the photovoltaic cell extending along the entire length of the first main face or the second main face in a direction from the first side face to the second side face the first electrically conducting wire element being embedded into the first groove.
 2. The photovoltaic cell according to claim 1, wherein the first groove is a longitudinal groove.
 3. The photovoltaic cell according to claim 1, wherein a second cover is arranged on the second main face, the second cover including a second groove, and a second electrically conducting wire element is embedded into the second groove.
 4. The photovoltaic cell according to claim 3, wherein the second groove is a longitudinal groove.
 5. The photovoltaic cell according to claim 3, wherein the second cover and/or the first transparent cover are placed directly onto the semiconductor substrate.
 6. The photovoltaic cell according to claim 1, wherein one of the first or second electrical contact elements comprises a metal layer covering the semiconductor substrate.
 7. The photovoltaic cell according to claim 1, wherein at least one of the first or second electrical contact elements comprises a plurality of conducting arms arranged on the semiconductor substrate, said arms being designed to be in contact with or to connected to the first electrically conducting wire element.
 8. The photovoltaic cell according to claim 1, comprising a single semiconductor substrate including a photovoltaic junction.
 9. The photovoltaic cell according to claim 3, wherein the second cover being transparent, the block comprises two semiconductor substrates including photovoltaic junctions separated by a metal layer, the photovoltaic cell comprising a third longitudinal groove for housing a third electrically conducting wire element designed to be connected to said metal layer.
 10. The photovoltaic cell according to claim 3, wherein the block comprises two semiconductor substrates including photovoltaic junctions separated by a dielectric, the photovoltaic cell comprising third and fourth grooves respectively formed on a side face of the photovoltaic cell at the interface between the dielectric layer and any of the semiconductor substrates.
 11. The photovoltaic cell according to claim 10, wherein on both sides of the dielectric a metal layer is interposed between the dielectric and any of the two semiconductor substrates.
 12. An assembly comprising a plurality of photovoltaic cells according to claim 1, the plurality of photovoltaic cells comprising first and second photovoltaic cells, wherein the first and second photovoltaic cells are connected to one another by several electrically conducting wire elements, each electrically conducting wire element being embedded within the first groove of the first photovoltaic cell and the first groove of the second photovoltaic cell.
 13. A photovoltaic cell comprising: a first external main face opposite a second external main face connected by a first external side face opposite a second external side face; a block comprising a photovoltaic junction; a first electrical contact element connected to a first pole of the photovoltaic junction; a second electrical contact element connected to a second pole of the photovoltaic junction opposite to the first pole; a first electrically conducting wire element connected to the first electrical contact element or the second electrical contact element; a first transparent cover arranged on the first external main face; and a groove in an external face of the photovoltaic cell extending along the entire length of at least one of the external main faces in a direction from the first external side face to the second external side face, said groove comprising a bottom and two side walls, one of the side walls being formed by the first transparent cover and the other side walls and/or the bottom being formed by the block, and the first electrically conducting wire element being embedded into the first groove.
 14. The photovoltaic cell according to claim 13, wherein the first groove is a longitudinal groove.
 15. The photovoltaic cell according to claim 13, wherein a second cover is arranged on the second external main face the second cover including a second groove, and a second electrically conducting wire element is embedded into the second groove.
 16. The photovoltaic cell according to claim 15, wherein the second groove is a longitudinal groove.
 17. The photovoltaic cell according to claim 15, wherein the second cover and/or the first transparent cover are placed directly onto the semiconductor substrate.
 18. The photovoltaic cell according to claim 13, wherein one of the first or second electrical contact elements comprises a metal layer covering the semiconductor substrate.
 19. The photovoltaic cell according to claim 13, wherein at least one of the first or second electrical contact elements comprises a plurality of conducting arms arranged on the semiconductor substrate, said arms being designed to be in contact with or to connected to the first electrically conducting wire element.
 20. The photovoltaic cell according to claim 13, comprising a single semiconductor substrate including a photovoltaic junction.
 21. The photovoltaic cell according to claim 15, wherein the second cover being transparent, the block comprises two semiconductor substrates including photovoltaic junctions separated by a metal layer, the photovoltaic cell comprising a third longitudinal groove for housing a third electrically conducting wire element designed to be connected to said metal layer.
 22. The photovoltaic cell according to claim 15, wherein the block comprises two semiconductor substrates including photovoltaic junctions separated by a dielectric, the photovoltaic cell comprising third and fourth grooves respectively formed on a side face at the interface between the dielectric layer and any of the two semiconductor substrates.
 23. The photovoltaic cell according to claim 22, wherein on both sides of the dielectric a metal layer is interposed between the dielectric and any of the semiconductor substrate.
 24. An assembly comprising a plurality of photovoltaic cells according to claim 13, the plurality of photovoltaic cells comprising first and second photovoltaic cells, wherein the first and second photovoltaic cells are connected to one another by several electrically conducting wire elements, each electrically conducting wire element being embedded in the first groove of the first photovoltaic cell and the first groove of the second photovoltaic cell. 